1. Field of Invention
This invention is directed to a printing system for delivering high-resolution images on vertical surfaces of recording media having a non-negligible third dimension.
2. Description of Related Art
A variety of printing methods are familiar to most people, including offset, letter press and gravure lithography, inkjet printing, laser printing, and impact printing. A technique that has nearly vanished over the past 20 years is mimeography.
Mimeography was widely used in the 1940s and 1950s in schools, hospitals and the military as an alternative to commercial printing. Traditional mimeography is inexpensive and can be accomplished “in house” with little capital investment and a high level of flexibility. A user needs only a typewriter or an impact printer, a mimeograph printer, which is about the size of a small photocopier, stencils, ink and paper. The heart of the traditional mimeograph system is the stencil, which is traditionally made of a natural fiber tissue and coated to block the flow of ink. To create an image, the stencil is placed in a typewriter. The typing keys remove the coating on impact. The stencil is then mounted on the mimeograph print cylinder. Ink, flowing from inside the cylinder through a porous metal cylinder surface and then through the voids created in the stencil by the typewriter, transfers the image to the paper substrate. Print quality is not comparable to typed memos or letters. As a result, use of the traditional mimeograph process was limited in commercial offices. Schools, hospitals and the military used this traditional mimeograph process because the copy is legible, but more importantly, inexpensive.
Mimeography in its original form has virtually disappeared in the industrial world. It has been largely replaced by photocopier equipment. However, recently mimeography was reborn when a “digital stencil” was developed. Digital stencils are made of a non-woven backing of natural and polyester fibers laminated to a polyester thin film of about 6-8 gauges. The digital stencil is imaged by using thermal printheads such as those used in facsimile machines and a wide variety of label printers. Such thermal printheads have a resolution of about 200 to 600 dots per inch. The digital stencil system, also known commercially as a digital duplication system, offers vastly improved print quality over traditional mimeograph equipment.
Thermal printheads accept digital data. As a result, stenciled images may be created in computers or digital scanners, as opposed to old-fashioned typewriters and impact printers. From the standpoint of print quality, digital duplicator systems are not comparable with photocopying. However, the improved print quality and low operating cost is useful in many traditional office settings.
The typical digital duplicator looks and performs very much like a small photocopier. An original image is placed on the machine's plate scanner, which scans and digitizes the image and downloads a copy to a thermal imager. The thermal imager burns holes in a plastic stencil at 300 or 400 dots per inch. The stencil is automatically loaded onto the print cylinder and paper is automatically fed into the printer, printed and discharged. The operator need only enter the quantity of copies desired and select the print speed. In some machines, a computer can be used for the digitizing process where an original does not exist. Thus, the operator can create an image having text, graphics, and the like on a personal computer and download the image directly to the thermal imager to start the automatic printing process.